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"LWRES_GABN" ("3") | C library functions | Unix Manual Pages | :man


lwres_gabnrequest_render, lwres_gabnresponse_render, lwres_gabnrequest_parse, lwres_gabnresponse_parse, lwres_gabnresponse_free, lwres_gabnrequest_free - lightweight resolver getaddrbyname message handling




#include <lwres/lwres.h>

lwres_result_t lwres_gabnrequest_render(lwres_context_t *ctx, lwres_gabnrequest_t *req, lwres_lwpacket_t *pkt, lwres_buffer_t *b);

lwres_result_t lwres_gabnresponse_render(lwres_context_t *ctx, lwres_gabnresponse_t *req, lwres_lwpacket_t *pkt, lwres_buffer_t *b);

lwres_result_t lwres_gabnrequest_parse(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt, lwres_gabnrequest_t **structp);

lwres_result_t lwres_gabnresponse_parse(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt, lwres_gabnresponse_t **structp);

void lwres_gabnresponse_free(lwres_context_t *ctx, lwres_gabnresponse_t **structp);

void lwres_gabnrequest_free(lwres_context_t *ctx, lwres_gabnrequest_t **structp);


These are low-level routines for creating and parsing lightweight resolver name-to-address lookup request and response messages.

There are four main functions for the getaddrbyname opcode. One render function converts a getaddrbyname request structure — lwres_gabnrequest_t — to the lighweight resolver’s canonical format. It is complemented by a parse function that converts a packet in this canonical format to a getaddrbyname request structure. Another render function converts the getaddrbyname response structure — lwres_gabnresponse_t — to the canonical format. This is complemented by a parse function which converts a packet in canonical format to a getaddrbyname response structure.

These structures are defined in <lwres/lwres.h>. They are shown below.


typedef struct lwres_addr lwres_addr_t;
typedef LWRES_LIST(lwres_addr_t) lwres_addrlist_t;

typedef struct {
lwres_uint32_t flags;
lwres_uint32_t addrtypes;
lwres_uint16_t namelen;
char *name;
} lwres_gabnrequest_t;

typedef struct {
char *realname;
char **aliases;
lwres_uint16_t *aliaslen;
lwres_addrlist_t addrs;
void *base;
size_t baselen;
} lwres_gabnresponse_t;

lwres_gabnrequest_render() uses resolver context ctx to convert getaddrbyname request structure req to canonical format. The packet header structure pkt is initialised and transferred to buffer b. The contents of *req are then appended to the buffer in canonical format. lwres_gabnresponse_render() performs the same task, except it converts a getaddrbyname response structure lwres_gabnresponse_t to the lightweight resolver’s canonical format.

lwres_gabnrequest_parse() uses context ctx to convert the contents of packet pkt to a lwres_gabnrequest_t structure. Buffer b provides space to be used for storing this structure. When the function succeeds, the resulting lwres_gabnrequest_t is made available through *structp. lwres_gabnresponse_parse() offers the same semantics as lwres_gabnrequest_parse() except it yields a lwres_gabnresponse_t structure.

lwres_gabnresponse_free() and lwres_gabnrequest_free() release the memory in resolver context ctx that was allocated to the lwres_gabnresponse_t or lwres_gabnrequest_t structures referenced via structp. Any memory associated with ancillary buffers and strings for those structures is also discarded.


The getaddrbyname opcode functions lwres_gabnrequest_render(), lwres_gabnresponse_render() lwres_gabnrequest_parse() and lwres_gabnresponse_parse() all return LWRES_R_SUCCESS on success. They return LWRES_R_NOMEMORY if memory allocation fails. LWRES_R_UNEXPECTEDEND is returned if the available space in the buffer b is too small to accommodate the packet header or the lwres_gabnrequest_t and lwres_gabnresponse_t structures. lwres_gabnrequest_parse() and lwres_gabnresponse_parse() will return LWRES_R_UNEXPECTEDEND if the buffer is not empty after decoding the received packet. These functions will return LWRES_R_FAILURE if pktflags in the packet header structure lwres_lwpacket_t indicate that the packet is not a response to an earlier query.



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